<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn01">我是一个按钮</button>
    <script>
        // document.getElementById()    根据id来获取元素
        var btn = document.getElementById("btn01");
        // innerHTML    HTML中的内容
        btn.innerHTML = "sssss";
    </script>
    
</body>
</html>